This invention relates generally to transceiver architecture in a wireless portable communication device.
Radio frequency (RF) transmitters are found in many one-way and two-way communication devices, such as portable communication devices, (cellular telephones), personal digital assistants (PDAs) and other communication devices. An RF transmitter must transmit using whatever communication methodology is dictated by the particular communication system within which it is operating. For example, communication methodologies typically include amplitude modulation, frequency modulation, phase modulation, or a combination of these. In a typical global system for mobile communications (GSM) mobile communication system using narrowband time-division multiple access (TDMA), a Gaussian minimum shift keying (GMSK) modulation scheme is used to communicate data.
The deployment of new wireless systems presents unique challenges to mobile handset designers. In order to reap the full benefit of expanded capacity and increased data bandwidth, the new handsets must work on both the new systems as well as the old. One of these new systems has been named Enhanced Data Rates for GSM Evolution (EDGE). The EDGE standard is an extension of the Global System for Mobile Communications (GSM) standard.
The EDGE standard increases the data rate over that available with GSM by sending more bits per RF burst. More bits are sent in EDGE by using a modulation scheme based on 8-phase shift keying (8PSK), which provides an increase over GSM's Gaussian minimum shift keying (GMSK) modulation format. In the EDGE modulation scheme, the 8PSK constellation is rotated ⅜ radians every symbol period to avoid problems associated with zero crossings. In contrast to GMSK's constant amplitude envelope, the EDGE modulation scheme results in a non-constant amplitude envelope. This non-constant amplitude in the output signal presents some difficulties with regard to RF power control.
During multi-slot operation of a mobile handset transmitter using 8PSK modulation, the power of the modulated radio-frequency (RF) signal is required to ramp-up to a desired power level for a set period of time during which the handset transmits encoded data symbols. After the transmission has completed, the power of the modulated RF signal is required to return or ramp down to an off power level. The ramp-up and ramp-down must be accomplished without adversely affecting time and frequency parameters defined by the EDGE communication standard.
One conventional approach to power control generates a signal that is used to controllably adjust the gain of a variable gain amplifier located in series with a linear power amplifier. For polar loop transmitter architectures, which are already operating near saturation in 8PSK mode, power control has been accomplished through power amplifier bias controls. These conventional power controllers require integrated circuit space, increase the power budget of the mobile handset and for some conditions require a longer time than that available to meet frequency spectrum requirements.
Another approach is introduced in U.S. Patent Application Publication 2005/0249312 to Bode et al. (the '312 publication). The '312 publication describes a digital modulator that introduces dips in the envelope of the I/Q signal between adjacent time intervals or bursts. A dip-shaped waveform is multiplied with each of the I and Q waveforms to introduce the dips. A pulse-shaping filter is used with the dip-shaped waveform to obtain the desired result in the envelope of the I/Q signal. This solution requires additional memory to store the dip waveform and integrated circuit space to implement the pulse-shaping filter.
Therefore, it would be desirable to provide dynamic power control in a mobile handset in an economic and efficient manner and in accordance with the EDGE communication standard across a broader range of operating conditions absent additional memory capacity or shaping filters.